Alternating current switching device



Feb. 19, 1957 F. KESSELRING 2,782,345

ALTERNATING CURRENT SWITCHING DEVICE Filed March 18, 1953 s Sheets-Shet 1 EI 1i IN VEN TOR.

Feb. 19, 1957 F. KESSELRING 2,782,345

ALTERNATING CURRENT SWITCHING DEVICE Filed March 1a, 1953 s Sheets-Sheet 2 IN VEN TOR.

Feb. 19, 1957 F. KESSELRING 2,732,345

ALTERNATING CURRENT SWITCHING DEVICE Filed March 18, 1953 3 Sheets-Sheet 3 G)! 4 6; fl 56 W INVENTOR.

Fe: Kasaewe United States Patent ALTERNATING CURRENT SWITCHING DEVICE Fritz Kesselring, Zollikon, Zurich, Switzerland, assignor to FKG Fritz Kesselring Geratebau A. Bachtobei- Weinfelden, Thurgau, Switzerland, a corporation of Switzerland Application March 18, 1953, Serial N 0. 343,07 7

19 Claims. (Cl. 31711) This invention relates to a magnetic switching device and is more particularly directed to a novel switching apparatus having a voltage path in parallel with the switching unit.

In the prior art arrangements for magnetic rectifiers and other similar devices which have multiple contact make and break operations in relatively short periods of time, the problem of sparking and pitting at the cooperating contacts during disengagement always arises.

Heretofore so called commutating or saturable reactors were connected in series with the cooperating contacts in order to reduce the interrupting capacity of a switching means. In this arrangement, the rapid rate of decrease of the load current caused the sa'turable reactor to unsaturate and thereby present a high impedance in series with the switch device and load. That is, a step was created during which period of time the contacts could be safely disengaged with little or no sparking-or pitting.

However, this prior art arrangement has two main disadvantages. In the first place, it is essential to have a relatively long step period to insure sufficient time to initiate contact disengagement and insure that there is complete separation of the cooperating members in order to prevent backfire or backflow of current. In order to make the device safety-proof, therefore, it was essential to extend the step period which resulted in reducingthe etliciency of the rectifying unit. In my novel apparatus, I achieve a substantially spark-free interruption without the necessity of a large commutating reactor and thereby increase the efficiency of the device. The second main disadvantage of the commutating or satura'ble reactor is its complexity and expense. The commutating or saturable reactors have circular iron cores composed of thin walled nickel iron. These devices are very expensive due to the high cost of the raw material, the thin gauge of the sheet metal which must be a few hundredths of a millimeter in thickness, the manufacturing difficulties encountered in winding the main current coil and the required auxiliary equipment such as the direct and alternating current biasing windings.

In the novel device of my invention, the above noted disadvantages encountered when using a commutating reactor are substantially eliminated.

In my novel apparatus, the current to be interrupted is intermittently sub-divided into component currents by means of parallel connections. That is, a current path and a parallel voltage path is provided for the flow of load current. The current path which is the branch wherein current interruption will take place is provided with a series rectifier which is designed for only a fraction of the source and load voltage but is capable of withstanding the total load current.

In parallel with this switching rectifier current path is a voltage path which is provided with rectifying'me'ans. This series rectifier in the voltage path differs from'the Series rectifier in the current path in that it is designed to" ice be capable of withstanding negative breakdown voltage equal to the maximum voltage of the source although it is only capable of withstanding a fractional portion of the load current.

In addition to the rectifying unit in the voltage path, a series inductor is provided, Although the current will divide between the current and voltage paths are predetermined times within the operating cycle, the circuits are designed; so that the current llow in the current path will lead to total current. This arrangement insures that the current flowing through the current path will pass through current zero prior to the time that the total current passes through the current zero. Thus, the device is so arranged that circuit interruption in the current path will commence immediately following the current zero therein to thereby insure substantial currentless interruption. That is, whereas in the prior art it was essential to provide a commutating reactor in series with the interrupting means to achieve a step current during the switching operation, the instant invention provides a parallel path in such a manner that the current flow in a current pathis Zero at the time of circuit interruption without the necessity of a commutating reactor.

Thus, it will be noted that the current path can successfully interrupt the circuit under current zero conditions and during the opening operation, the rectifier in the voltage path will prevent backflow of current. In this novel arrangement the current flow in the current path is relatively large during the major portion of the operating cycle.

Since the novel apparatus merely requires that a lagging current flow in the voltage path only immediately preceding and during the current interruption, additional means can be provided to achieve this effect. That is, rather than have current flow through the voltage path during the'major portion of the effective cycle of operation and introduce additional losses, means may be provided to insure that current flows through this current path only when it is essential to have current zero interrupting the operation.

Thus, my invention also sets forth a novel arrangement wherein the IR losses in the voltage path will be maintained at a minimum by providing means which will divert the current to this voltage path just prior to the zero passage of the total current. This is achieved by providing a rectifier unit in the voltage circuit which may be triggered oif from the line circuit. That is, a controllable rectifier replaces the above mentioned rectifier in the voltage path. Thus, for example by providing a diode having a predetermined breakdown voltage, it is possible to supply the plate voltage thereof from predetermined current conditions in they load to thereby insure that this unit will breakdown from one to live milliseconds before the Zero passage of the main current.

As heretofore noted, one of the major problems of repetitious circuit interruption for magnetic rectifiers and other switching devices is the burning and pitting of the contact material during current interruption. However, it, is not only essential to have substantially currentless interruption but it is also necessary to provide means to For installations which will be used with relatively large loads, a small saturable reactor may be inserted in series with the interrupting unit and rectifier of the current path to thereby create a short step during current interruption. It will be noted that since the voltage parallel path provides a substantially currentless interruption that the additional above mentioned saturable reactor will not have to be a large complex unit and hence, the losses introduced thereby and the expense thereof will be relatively small as compared with the prior art commutating reactor type of magnetic rectifier.

It will also be noted that my device may be provided with an arrangement wherein a small commutating reactor can be provided for the voltage path.

In the operation of magnetic rectifiers wherein many current interruptions must occur within a very short period of time and which requires that the voltage path be phase shifted from the current path results in an arrangement wherein a large current magnitude may be required in a current path in order to obtain sufiicient phase shift and hence, would require not only a large and expensive series rectifier therein but would also introduce large IR losses. Also due to the frequent period current variations in both the current and voltage path, large back E. M. F.s will be caused by the indnctances in each circuit thereby creating additional losses in the circuit. 7

In order to overcome the above mentioned disadvantages, a commutating reactor may be provided in the parallel voltage circuit to considerably reduce the speed of current variation in the vicinity of current zero passage thereby eliminating the above mentioneddecrease.

That is, a commutating reactor can be properly biased to be effective during the switching operation.

It will also be noted that losses may be introduced into the circuit due to the series rectifier of the current path since this rectifier must carry the full load current. However, these losses can be considerably reduced by providing a parallel saturable reactor for the series current path rectifier which is capable of diverting the current therefrom. Thus, during the major portion of the operating cycle, a substantial portion of the load current will flow through the winding of the saturable reactor and thereby be diverted from its parallel connected rectifier. That is, as is well known in the art, after a predetermined magnitude of load current has been reached, the saturable reactor will be saturated and present substantially no reactance to the circuit. Thus, during this condition, the cornmutating reactor will be similar to low inductance unit in parallel with the series rectifier to thereby relieve the rectifier from carrying a load current and hence, reduce the losses which would otherwise result. However, when the load current approaches zero the decrease in current magnitude and the rapid rate of change of the current will cause the reactor to unsaturate.

As is well known in the art, this will have the efiect of presenting a substantially large reactance or inductance to the circuit during the period when it is unsaturated. Hence, during this portion of the cycle, when the current is bridged and going through current zero, the reactor will be equivalent to a high reactance in parallel with the series rectifier and hence will not divert any current therefrom and hence, all of the load current will again flow through the series current path rectifier.

It will be noted that my novel invention although readily adaptable to the achievement of rectification of alternating current is not limited thereto.

In one modification utilizing the basic parallel path principle of my invention, it is possible to provide a fast acting alternating current switch. In this arrangement, the series rectifier in the current path is shunted during normal operation by a switching device. It is only during desired current interruption that the switching device is opened to thereby insert the series rectifier unit in series with the load. In this arrangement, the current interrupting means, although capable of interrupting maximum load current need only have minimum interrupting requirements due to the parallel voltage path. However, the series rectifying unit in the parallel voltage path is capable of withstanding the entire source reverse voltage.

Additional means may be provided in the voltage path such as a series switch which may be opened after the main line has been interrupted. This series voltage switch will open on a currentless line and relieve the voltage path rectifiers from blocking the source voltage.

Accordingly, a primary object of my invention is to provide a novel switching unit wherein current interruption can be achieved without the necessity of a large conimutating or saturable reactor.

Another object of my invention is to provide an alternating current magnetic switching means having a current and a voltage path wherein the design of the circuitry results in zero current flow through the current path during circuit interruption.

Another object of my invention i to provide a parallel path arrangement wherein the current in one path will lead the current in the second path so that interrupting means in the first path may be operated under substantially currentless operation.

A further object of my invention is to provide a novel rectifying unit which has relatively high etficiency.

A still further object of my invention is to provide switching circuitry which eliminates the relatively complex and expensive commutating reactors which were heretofore utilized in the prior art.

Another object of my invention is to provide novel circuitry wherein a rectifying unit having characteristics which enable it to carry large magnitudes of current although having a low negative breakdown voltage is operative only during the operating portion of the cycle and is effectively removed from the circuitry during the interrupted portion of the operation.

Another object of my invention is to provide novel circuitry for a switching device wherein a rectifying unit 1 having a high negative breakdown voltage and little capacity to carry large currents is effectively introduced in the circuit during the interrupted portion of the operation and effectively removed from the circuit during the major portion of the operating cycle.

Still another object of my invention is to provide switching means wherein maximum utilization of the desirable operating characteristics of the components is achieved.

A still further object of my invention is to provide a parallel path arrangement for rectifier units in which the IR drops of the parallel voltage and current paths are relatively small.

A still further object of my invention is to provide a novel circuit in which the losses of the various components thereof is maintained at an absolute minimum.

Still another object of my invention is to provide a voltage path in parallel with the switching current path which is triggered or rendered efiective immediately prior to and during the switching operation to insure maximum etficiency.

These and other objects of my invention will be apparent from the description when taken in connection with the drawings in which:

Figure 1 represents a circuit arrangement wherein my novel circuitry can be used for a magnetic rectifier. This Figure 4 isa voltage-current versus time curve-ofthe various electrical conditions existing-in the circuitry of FigureS.

Figure 5 is a current versus time curve illustrating the magnitude and time division of the current between the series current rectifier and the current path and its parallel saturable reactor. Figure 6 is a circuit illustration of the current and voltage path and illustrates circuitry which can bowed to reduceand eliminate return current flow through the switching apparatus;

Figure 7 is an illustration of an improvement which can be used with-the circuitry of Figure 1 or 3 to reduce or eliminate the undesirable back E. M. F. effect in the series'induct'or of the voltage path.

Figure 8 is a current-Voltage versus time illustration of' the electrical conditions existing in the circuitry of Figure7L Figure 9- represents a second electrical improvement which may be used to replace the arrangement of Figure 7 toreduce the losses and undesirable efiects in the series inductor of the voltage path.

Figure 10 is a current versus time curve illustratingthe electrical conditions existing in the circuitry of Figure 9.

Figure 11 is a circuit illustration of the manner in which my novel principle of parallel voltage in current paths may be applied to an alternating current switch.

Figures 1 and 2 illustrate my novel invention when used as a magnetic rectifier to convert the A. C. from the supply transformer Gila to D. C. for the load 10. The supply transformer 6% has a primary winding 61 and secondary windings 62 and 14. The secondary winding 14' of the transformer 60a is constructed so that the-voltage V0 obtained from the Winding 14 and a portion of the secondary winding 62 will lead the voltage V which is obtained solely from the secondary winding 62. The control of the current flow from the secondary 62 to the load 10 is achieved by means of the switching device 20.

It will be noted that the switching device is merely a schematic illustration of a switching unit similar to the one shown in Patent No. 2,732,451, dated January 24, 1956, and which-is assigned to the same assignee as the instant application. This unit has a bridging contact 30 which is biased to the open position by thespring 40.

The armature 3-1 is provided with a closing winding 60 which is energized from the auxiliary winding 14 and a portion of the secondary winding 62 as will hereinafter be more fully described.

The switching device 20 is also provided with a holding coil 50 which is in series with the load. A rectifier 70'is provided in series with the bridging contact 30 to complete the current path of the rectifier.

As will hereinafter be apparent, the rectifier I0 is capable of withstanding the full load current although it is not required to have a high negative breakdown voltage. Connected in parallel with the current circuit comprised of the bridging contact 3% and the current rectifier 70 is a voltage path connected at the terminals A and B. This voltage path is comprised of a small inductance 20 and voltage rectifiers 8%.

As will hereinafter be apparent, the voltage rectifiers 80 need not have the capacity to carry large load currents but instead have the characteristic of having a high negative breakdown voltage.

The closing winding 60 is energized through the circuitry comprising the 'left hand end of the secondary winding 62, the secondary winding 14, rectifier 12 and the adjustable rheostat 13.

The operation of the closing coil dtl'is as follows:

As best seen in Figure 2, the voltage V across the secondary winding 62 lags the voltage V0 which is obtained fromthe terminals of the supplementary Winding 14 and the left terminal of the secondary winding 62. Thus, at time tothevoltage Vo-Wlll bepassing through negative andsincreasingin thepositive direction.

avenge-sis The rectifier 12 will limit the current flow'in the closing winding 60 from the combined windings 14 and 62 to a direct current. The rheostat 13 can be adjusted so that the magnitude of current flowing through the 010sing winding 60 can be controlled. Thus, the rheostat 13 can be adjusted so that the required ampere turns to move the armature 31 and the bridging contact 30 to the closed position against the opening force of the biasing spring 40 will occur at time n. That is, in order to obtain maximum efiiciency, it is desirable to have contact engagement occur at the time that the source voltage V emanating from the secondary winding 62' passes through zero in the positive direction. Thus, the leading voltage V0 .in combination with the adjustable rheostat 13 will enable-thecontact 30 to close as soon asthe Zero passage of the. source voltage V occurs.

At a time ti, load current I will commenceto flow in the circuit. It will= be noted that. due to the inductance in the circuit from holding winding 50 and the: voltage winding 9tl'that the current I will not have an immediate high rate of rise. That is, instead of being a sinusoidal current, its immediate rate of'rise will be small. This is a verydesirable efiect since possible bouncing or chattering of the bridging contact 30 would create considerable sparking if the current magnitude was too high. Thus, by insuring thatthe current builds up slowly, undue bouncing or chattering of the contacts during theclosing operation will not cause sparking or pitting thereof due to the low magnitude of the current. I

It will be noted that while the current I is on the posi tive increase, practically no current will be permitted to flow in the voltage path due to the inductive ettect of the inductance 96. Thus, as illustrated in Figure 2, the current flow through the: voltage path during a substantial portion of the positive build up of the main current I is substantially zero. Hence, the current I1, flowing in the current path will be substantially equal to the current I flowing in the load. When the rate of increase of the load current'source starts to decrease, the inductor will tend to maintain the current flow and thereby divert current intothe voltage path. The current which is diverted into the voltage path from the point A is labelled Is, as seen in Figure 2.

As the load current I passes through its maximum value and the rate of decrease increases, the inductor 90 will tend to maintain the current at its present value and hence, an increasing amount of the load current I will be diverted into the voltage path.

Thus, as seen in Figure 1, from the time t1 when a current starts to flow in substantial amounts in the voltage path, during the time 22 the current diverted at point A through this voltage path will be continuously increased.

As best illustrated in the curve of Figure 2, it will be noted that during time t1 to t2, the bridging contact 30 is closed even though the voltage V0 is passing through the zero point during a portion of this period. That is, even though the closing coil 66 is not energized during the portion of the conducting cycle, the contacts 30 may be maintained closed by the holding coil 50 which is energized by the current I1.

Since the current I1 represents a major portion of the large load current, the ampere turns of this holding coil 50 will hold the bridging contact 30 with high pressure contact.

As best illustrated in the current curve of Figure 2, the current I1 flowing through the current path will lead the current I2 flowing through the voltage path. Asalready noted the currents' I1 and I2 are component parts of the load current I. Hence, since the load current I goes through the zero current point at time is and since the current 12 in the voltage branch lags the current I1 in the current path, the current 11 will have to pass through current zero at sometime prior to t3. As illustrated in the figures, the current I1 will pass through zero at time t2.

It will be noted that at this time t2, the current I2 will be equal to the load current. Thus, during the period between time t2 and t3, namely At, the current 11 in the current path will be zero.

Since the rectifier 12 prevents energization of the closing coil 60 during the negative half cycle of V closing coil 60 will not be energized during the period At. Also, since the current I1 is at zero value during the time At, the holding coil 50 will not be energized. Hence, the biasing spring 40 will be able to dominate the bridging contact 30 and thereby move it to disengaged position. Therefore, it will be noted that the switching operation occurring at sometime between the period At will occur with zero current through the bridging contact 30.

Since the contact separation can occur during the current zero period, even though a current I2 is flowing through the voltage path, complete separation of the cooperating contacts 30 can be achieved before there is opportunity for reverse current flow.

After there is complete separation of the cooperating contacts 30, the airgap will be sufiicient to prevent the negative voltage Vsp from causing reverse current flow. Hence, the current rectifier 70 will not have to have a high negative breakdown voltage. However, since the voltage path comprising the induct-or 90 and the rectifiers 80 remain in series with the source and load, the rectifiers 80 will have to have high negative breakdown voltage.

It should be noted that with the operation as described, the voltage rectifiers 80 do not have to sustain high load currents and are merely called upon to resist negative breakdown voltages whereas the current rectifier 70, although required to carry full load current, is not called upon to resist negative breakdown voltage.

Thus, at time 23 when the load current I is at current zero, the current and the voltage branch I2 will also have to be zero and hence, there will be complete interruption of the load current. This is true since from the time t2 to time Is, namely the period At, current I2 is equal to current I. Thus. in the above described operation, sub stantially currentless interruption is achieved without the necessity of a commutating reactor. At time t1, the above described cycle will be repeated when the contacts 30 are again closed. It will be noted that the length of the period At represents current zero through the current path and hence, it would be desirable to increase this period of time to enable complete circuit interruption during current zero interval.

However, as the time At is increased, the magnitude of the current 12 will also be increased and since this would represent larger current flow through a relatively high reactance voltage circuit, the losses of the rectifier would be increased. It is, therefore, desirable to use a substantially massless armature in the switching device 20 which could be the type of switching means discussed in Patent No. 2,732,451, assigned to the same assignee as the instant application which can effect circuit interruption in less than seconds.

Thus, it is possible to have circuit interruption accomplished at a very short interval following the time t2 and hence, the period At can be substantially reduced, as heretofore noted.

The maximum value of the current I2 will be dependent upon the period of time At and since a large current I: would represent losses in the voltage path, a fast acting switch unit which reduces the period At will greatly increase the efficiency of the rectifier.

Thus, it will be noted that the novel circuitry of my invention incorporates a current path and a voltage path wherein substantially current zero conditions exist in the obtain currentless interruption. In this arrangement, the

current rectifier does not have to withstand a high back voltage since it is in series with the interrupting contacts.

The voltage rectifier, although required to have a high negative breakdown voltage, is not required to carry any substantial amount of the load current. Thus, with this arrangement, currentless interruption is achieved without a saturable reactor and maximum utilization of the desirable characteristics of the circuit components is achieved.

The circuit diagram of Figure 3 and its associated current voltage curves of Figure 4 illustrate an improvement of the circuitry of Figure 1.

At large magnitudes of voltages and currents, the IR losses in the voltage branch of the rectifier will be relatively large and thus, substantially reduce the efficiency of the rectifying device. In order to correct and avoid this situation, it is desirable to have a circuit arrangement wherein the voltage circuit is rendered inoperative during a major portion of the operating cycle and is triggered off only at a predetermined time which is immediately prior to the current-zero time of the current in the current path.

An arrangement wherein the voltage circuit can be triggered at a predetermined time is illustrated in the improved circuitry of Figure 3. In this arrangement, the switching apparatus 30 is schematically illustrated only as a simple switch and the magnet construction, closing and holding coils are eliminated for the sake of simplicity.

The voltage rectifier of Figure 1 is replaced by the gas filled diode 27 in Figure 3. An additional component 20 is provided for the control of diode 27. The component 20 has an iron core 21 having an air gap 22 and a primary winding 23, a secondary winding 24 and a biasing or pre-excitation winding 34.

The pre-excitation winding 34 insures that the saturable core 21 will be saturated at the commencement of current flow, namely t1. At the time t1, no voltage will be induced into the secondary 24 of the saturable transformer 20 since there is no change of flux. Hence, during this period of time, there will not be suflicient plate voltage for the diode 27 and there will be no flow of current through the voltage circuit.

Accordingly, from time t1 to time tz, the load current I will be equal to the current 11 in the current path. At the time tz when the current I flowing through the primary 23 of the saturable transformer 20 is decreasing, the core 21 will become unsaturated. At this time, a voltage will be induced in the secondary winding 24 thereof.

The voltage induced in winding 24 at time tz is of proper polarity to permit current flow through the rectifier 25 to thereby charge the condenser 26. Hence, the voltage of the condenser 26 will now represent plate voltage of the gas diode 27.

The circuitry and components are properly designed so that the condenser 26 will supply a sufiicient plate voltage to the gas filled diode 27 to cause the diode to breakdown and permit current flow through the voltage path.

Thus, at time to which is immediately prior to the current zero time of the current I1 through the current path, the voltage circuit will be triggered to render it eifective. As current I2 commences to fiow in the voltage branch at time tz, the total load current I will be equal to current I1 and I2.

It will again be noted that the current I2 of the voltage branch will lag the current I1 of the current branch. Thus, the current 11 will pass through zero at time In which is a period At prior to the time is when the current I2 of the voltage branch or the total current voltage 1 passes through current zero. Thus, at time t2, the current 12 will be equal to the current I and the current 11 in the current branch will be zero. Hence, the current eese;

v n'gco'ntacts 30 during the time of rseparaon s substan ally Zero. 7 I "Furthermore, it"will be'noted "thatth'e "rateof increase or the an em '12 from the time into the time tzwill be much less thanthe rate of increase'as noted in'the circuitry of Figure 1. This resuItwiIl'bedu'e to'the effect of the reactor 20 and hence, 'since the current 12 flows for a shorter length of time, and has "smaller maximum Yaliie' thtihjthdtreached intlie arrangement of Fig'iil 'e 1, the lossesfin thejvoltag'epath will be considerably reiiiiced. Thusgwith the novel circuitry'of Figure 3, the losses in the voltagepathbecome negligibly small.

t will be noted "that the "gas filled diode 27 can b 'febl a'cedwith a gas triode whereby the voltage circuit v can be triggered eas connecting the secondary Winding 24 across thel'gridcathode circuit of the triode. It will be noted off'cou'r'sejthatfthediode 27 or a triod e which j'iriay be used toffeplac'e it will "not have to conduct the load'curreritahd hence, ne'ed 'noth'ave the largemag'ni- 'tude current carrying characteristics of the rectifier $0. I, Howeverjthismnitwill havetobe capable of sustaining the 'full back voltage and thus have the characteristic of ahigh negative breakdown voltage.

The circuitry'ofFigure 3 also illustrates another in:- s'provement over "that shown in Figure 1. Inthis arfrangernent, thefrectifie'r 3 1, which eom'par'es to the rectifier 70 of Fig't'lre '1 is provided with "a "sa'tur'able core 32 33 in parallel therewith.

Thecurje'nt curve characteristicsjo f" this "portion of the circuit is' illustrated in Figure '5. The ar angement tor "byrna'ssingthe'ciifrent diode 31is jirovided for thesole f rpbsefofr H tig the niaidmiimload current capacity "reqhirelhenvor thisrctifi'er. g w

r The sequence of operation of this parallel satprable eore in cobrdi'ria'tionfwith the rectifier :31 is as follows: w ntheldadciirrnt llcotiirnences to flow in the'circuit a ti'r'r'ie tijthereacwr 32'will be'uhs'atur'ated and hence, "will represent a la'rge impedance to" the circuitas is well known-mutant. g

Thus during this period of time, therefwill be an eflective 'lafge im'fiedance in p'arallel' with thejiectifie'r 31 entl thusjalllo the lo'a'd"currehtlfwilllflow through "the 'retifier 31. Thatisjwhenltheswitchfi'ltlfisfirstj closed, all" of the than current will flow g through the rectifier 31 before the reactor 32 is=saturated. A F The current 'llowihg through therectifier 31 is identified as} 131 in the current "curve of Figure 5 However; "after as on interval of"time,' 'namelyat tirnete, thereactor32 willbeconie'sat'urated. v x A husratt-imefa'wh'enthe current llhZlS reached a suffficie'rit inagnitude'to saturate the "reactor 32; the winding '33 will be an efie'ct'ive short' circuitfacross rectifier 31. Thus, as best seen in figure 5,the"divisi onof" current betweenthe" twouniits willbfe' such thata 'majorpo'rtion ot the; current ll "will flow through the winding 33 (as shownby lst) a d very litfle"currentwill fiowthrou'g h t-he'itifiefiit ownfby no. y

Accordingly, during thefinaj or portion of 'the" cyclejof "'op eration of the" magnetic rectifier, the rectifier 31fwill be substantially short 'circuited by the winding 33" du'eto the saturated condition of the reactor32. v

Near meanest the cond1i"c'tin cycle, namelyet time t1, the "reactor 32will 'be'comeuns urate'd and hence,

'fji'r eserit" a high 'ir'nfiedance td this circuit as is well known in -the art.

"At this hoint, the current division between the components 31 and '33 willagain changes nc'e the-reactor'32 -will represent a large impedance in" para-net with the rela- 'tivel y s'mall iinlidance "or theg rectifier 31. "Thus, hetEveen ti 7 t'1 a'nd t2,-as seen in Figure 5,"arnajor"portion eetueeurtem I1 will now'tm-ou n the rectifier 31 (iden- 'ti fied as I31), and l ittle or no' current "wilhfiow t'hrough the s uance-w nd n s; g I

It will beno-t'edby utilizing this parallel reactor 32, as a switching device to alternately divert theourrentto the conducting'cyeleis relatively small 'the 1R drop there- 'a'cross jwillals'o be'very small "even "though the magnitude of I1 should reach great ip'roportions. Y

Additional meansma'y be 'provided'in order to limit the back currentfio'w in the' circuitr'y from'the time 12 to thetime t1*. n

It will "be noted that heretofore, "a large commutating or 'satura'ble reactor is used in series with the circuits providing a 'relativelylongstep circuit to insure complete separation of the contacts during the stepan'd at a step immediately following theseparation'inorder to eliminate backflowofcu'rrent. I

As heretotorenotedrthe'contacts of my'novel circuitry yopen's under substantially current zero conditions and hence, thepossibility of reversecur-rent flow is relatively small due to'thesafetyberio'd At. Howevenas an added precautionto insure that therewill be no backfiow of current, asinall saturable reactor 29 may be inserted in the current path. I

The saturable reactor 29 can be pie-magnetized (not shown) ina manner wellkno-wn in the artso that a step current will occurd'urin'g the switching operation.

It will be "noted thatin'theimproved circuit design of figure 3 wherein a gas tube 27is substituted for'the "rec't'ifierstit),"the overalliefiiciency of the switching "circuit "cianbe' improveddueto the reduced IR losses. Thus, for

example, asshrpingthat"withthe usle ot' dry rectifiers'flil,

losses can fl'ieeliminated'by using a gas filled tube as slio'vi/nfin Figure "3. Thtisfif twofrectifierstltl are re- *p-ncea by a s'ingle"gas tilled tube rthe efficiency can be increased to 92*ari'd /2 percent. It the number of dry "re'ctifie'rs' 8 0require d' inthecir-cuitry'of Figure 1 is five, the'e'fficienc'y of't he circuit shown in Figure 3 by replacing 'the-fiVe'dry"reetifiersfwith asingle gas filled tube 27 can b'e-iiic-feased to 97%. "Accordingly, the'arrangement of Figure? is much rnore"eco'nomicaland obtains a much higher efli'cienc'y than the circuit arrangement of Figure 1.

A 'niodified' arrangenientwhereby the hack current rfiowin'g through cooperating contacts 30 can be reduced is illu'strate only a" po"r't 1'on of the-circuitry shown in Figure 1 but is "iirovided wi eouples the inFigure 6. This arrangement illustrates tHe add'itionaI transformer unit 16 which t-"efind'wol-tage paths.

The transformer 16 has a primar'y winding which is 'in 'serie's with the 'voltagejath'and serves thed-ual =func't'ion-"of energizing 'the transformer -16 and performs "the samdfunct ien'as the inductor 90"as seen inFigure l.

The"transforrner -has-a "sec'o'n'dary winding 17 which is *connected 'i n 's'eries'with' 'thefvar'iab'le resistor 17 and in L zii'aHeI'y'Vith the eondenser 19 and the cooperating con- The operationofth'is unit 'isas follows: commencing at timetz until timeva asse'en in- 'Figure 4, the current I2 in'the voltage'pa'th willbe' decrea'sing at a constant rate. Accordingly, a substantially constant'direct current potential"will be introduced into the secondary winding 17 due to the' COnsta'nt rate of decrease of'the current I2.

By proper adjustment of the variable impedance 17,

the commutating current In resulting from the induced in thesecondary'winding 17 can be made substantially equal to the 'back'or return current Ir of the 'rectifier70. -That is,' the"syste'm is's'o arranged that the current In will compensate' for the back or return current 11' 7 across the cooperating contacts 30.

w Further iinpi-ovements overthe' arrangement shown in Figure 3' to inerease'the 'e'thciencythereof are'shown in "Figures T and9 and "explained'by' the use of the current curves of FiguresSand 10.

The inductance 28, connected in series with the voltage path, will have a back E. M. F. which will be detrimental to the circuit. That is, during the period At from time 22 to is, when the current I2 in the voltage branch is decreasing, an inductor 28 will tend to maintain the current at its present value and hence, a large back E. M. F. will result therein. The arrangement shown in Figures 7 and 9 provides a circuit whereby the inductor can be short circuited at this predetermined period of time in order to eliminate its undesirable effect on this circuit. Thus, for example, as seen in Figure 7, a diode 40 can be placed in parallel with the inductance 28.

During the period of time from is to la when the current I2 is increasing, the voltage V will be negative across the diode 40 and hence, there will be no conduction therethrough.

However, at the time Is when the current I1 is at current zero, the current I2 will commence to decrease.

The induced E. M. F. will be of proper polarity to break down the tube 40. That is, the voltage V will now be positive as indicated by V' and hence, there will be conduction through the diode 40. Accordingly, the diode 40 will now represent a substantial short circuit across the inductor 28 and thereby render this unit practically ineffective.

A modified arrangement of that shown in Figure 7 is illustrated in Figure 9 wherein the inductor 28 serves as a primary winding for the transformer 42. The secondary winding 44 and the transformer 42 is connected in series with the rectifier 45.

Thus, for example, from the time tz to the time ta when the current I2 is increasing as shown in Figures 4 and 10, the rectifier 45 will block any flow of current from the secondary 44. Hence, the equivalent circuit during this period of time from tz to t2 will be a high impedance across the inductor 28. However, at time t2 when the current I2 in the voltage branch commences to decrease following the time t3, the voltage induced in the secondary winding 44 of the transformer 42 will be of proper polarity to permit conduction through the rectifier 45. This of course will represent a short circuit on secondary winding 44, the equivalent circuit thereof being a short circuit across the primary winding 28.

Accordingly, the novel arrangement shown in Figures 7 and 9 will induce a substantial short circuit across the inductor 28 during the period At to eliminate any undesired etfect at the back of the E. M. F. of this unit.

Figure 11 shows an arrangement whereby my novel parallel voltage current path arrangement can be utilized in connection with an alternating current switch.

In the circuitry of Figures 1 and 3, the arrangement is designed primarily for use with a rectifying unit whereas in the arrangement shown in Figure 11, the principle and concepts of my invention are applied to a circuit interrupting device. In this arrangement, there is current flow from the source 50 to the load 63 through point A of the stationary contact 52, the movable contact 54 to point B. Thus, during normal operation, the rectifier 58 in the current path and the rectifiers 59 and in the voltage path are not introduced in the circuit. The movable contact 54 is pivoted at point 62 and may be controlled by the solenoid 55.

For the sake of simplicity, the energization of the opening coil 55 is illustrated as being achieved by the series circuit members, the battery 56 and the closing circuit 57.

It will be noted that the opening coil 55 may be energized in any desirable manner. Thus, for example, it can also be energized from the load current and be responsive to predetermined overload conditions.

When the solenoid 55 is energized, it attracts the arm of the movable contact downwards so that it rotates in counterclockwise direction around the pivot 62. This will immediately divert current flow from the arm 54 to the path consisting of the arcing horns 52, 53 and the cur- 7 rent rectifier 58.

12 That is, current I1 will now flow through the arcing horns and the rectifier in the current path. -Since additional impedance has been introduced into the current path, some of the load current I will be diverted to the voltage path and thus, a current Iz will flow through the voltage rectifier 59.

Since the magnetic field of the arc Will tend to blow the arc existing between the arcing horns 52 and 53 upward, there will be complete interruption of the current in the current path when the current I1 passes through current zero since rectifier 58 will prevent reverse current flow.

The current 12, which lags current I1, as heretofore noted in connection with the Figures 1 and 2, will pass through current zero at a period At following the interruption in the current path and reverse current will be prevented from flowing due to the rectifiers 59.

Thus, during this following half cycle, the switch 60b may be opened under currentless conditions to achieve complete interruption of the circuit. It will be noted that the pivot arm 54 and the connecting link 61 of the switch 6% may be inter-connected with the lost action as is wellknown in the art so that the cooperating contacts 60b open in a period in excess of At following the disengagement of the cooperating contacts 52, 54 by solenoid 55. Accordingly, after the two switches 51 and 60b have been opened the current circuit is completely interrupted.

Thus, in essence, my invention relates to a novel method of circuit interruption wherein a current path containing the main cooperating contacts for circuit interruption and a current rectifier is shunted or bridged by a voltage path containing a voltage rectifier and an inductance.

By proper component design or adjustment, the current in the voltage path can be maintained at substantially zero value during a major portion of the operating cycle and commence to flow and lag the current in the current path immediately prior to current zero conditions thereof.

Thus, by making the switching apparatus in the current path an electromagnetic switch device, the cooperating contacts can be disengaged under substantially currentless conditions even though there continues to be a slight current flow in the voltage path.

After the current flow in the current path has reached current zero conditions, the voltage rectifier will prevent reverse current flow therein and since the electromagnetic switch is completely opened, there will be no reverse current flow in the current path. Hence, complete interruption of the circuit is achieved with sparkless operation of the cooperating contacts without the use of a commutating reactor.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein but only by the appending claims.

I claim:

1. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier.

2. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, said voltage rectifier capable of withstanding full negative voltage of said source.

greases 3. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load,'said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, and means to render said first circuit effective immediately prior to current conditions in said current path.

4 In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, the total current flowing from said sourflce to said load divided between said current path and said first path at a predetermined time within the operating cycle in such a manner that the current through the first path lags the current through the current path; i

I a switching device ha ing a first path and a cure Pa h i Paral el said parallel c mb a ion of said fi t an cur n paths ng i se ies wi a source and Iced, i u ren pa h comprising an el r m gne ic switching device and a current rectifier, said first path containing an inductor and a first rectifier, and means to render said first circuit effective immediately prior to current conditions in said current path, said electromagnetic switch interrupting the circuit at substantially currentless conditions.

6. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, and means to render said first circuit effective immediately prior to current conditions in said current path, said electromagnetic switch opening when the current flow in said current path is at current Zero.

7. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, said first path rendered ineffective during the major portion of the operating cycle.

8. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, said first path being an infinite impedance during the major portion of the current conduction through said last mentioned path.

9. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, said first path rendered ineffective during the major portion of the operating cycle.

10. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, the load current from said source to said load divided between said current path and said first path at a predetermined time prior to current zero in said current path.

11. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and 'a current rectifier, said first path containing an inductor and a first rectifier, said first rec'- tifier being a gas diode, means to control the plate voltage of said diode, said means rendering said diode non-conductive during the major portion of said cycle in said circuit.

12. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, said first rectifier being a gas filled'tube, means to control the conductivity of said gas filled tube, said means rendering said gas filled tube operative immediately prior to current zero condition in said current path.

13. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, means to render said first rectifier effective, said means comprising a saturable transformer having a primary and secondary winding, said primary winding of said saturable transformer connected in series with said source and said load, said sepondary winding connected in series with a rectifier, said rectifier poled to prevent current flow through said secondary winding when said primary winding is energized by an increasing current.

14. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, the total current flowing from said source to said load divided between said current path and said first path at a predetermined time within the operating cycle in such a manner that the current through the first path lags the current through the current path, a saturable reactor having a primary winding, said primary winding of said saturable reactor shunting said current rectifier, said primary winding effective as a substantially short circuit across said current rectifier during the major portion of a conducting cycle of said circuit.

15. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, the total current flowing from said source to said load divided between said current path and said first path at a predetermined time within the operating cycle in such a manner that the current through the first path lags the current through the current path, means to short circuit said inductor when the current through said first path is decreasing.

16. -In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic switching device and a current rectifier, said first path containing an inductor and a first rectifier, the total current flowing from said source to said load divided between said current path and said first path at a predetermined time within the operating cycle in such a manner that the current through the first path lags the current through the current path, means to short circuit said inductor when the current through said first path is decreasing, said means comprising a diode connected in parallel with said inductor, said diode operated for current induction only during current decrease in said inductor.

17. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current paths being in series with a source and load, said current path comprising an electromagnetic, switching device and a current rectifier, said first path containing an inductor and a first rectifier, the total current flowing from said source to said load divided between said current path and said first path at a predetermined time within the operating cycle in such a manner that the current through the first path lags the current through the current path, means to short circuit said inductor when the current through said first path is decreasing, said means comprising a transformer having said inductor as a primary winding thereof, a secondary winding for said transformer, said secondary Winding connected in series with a rectifier, said last mentioned rectifier operated to prevent current flow through said secondary winding when the current flow through said primary winding is increasing.

18. In a switching device having a first path and a I current path in parallel, said parallel combination of said first and current path being in series with a source and a load, said current path comprising an arc extinguishing means and a current rectifier, said first path containing a first rectifier, said are extinguishing means and said current rectifier normally bridged by a movable contact, opening means to remove said movable contact parallel path from said arc extinguishing means and said current rectifier to thereby divert current from said source through said current path and said first path.

19. In a switching device having a first path and a current path in parallel, said parallel combination of said first and current path being in series with a source and a load, said current path comprising an are extinguishing means and a current rectifier, said first path containing a first rectifier, said arc extinguishing means and said current rectifier normally bridged by a movable contact, opening means to remove said movable contact parallel path from said arc extinguishing means and said current rectifier to thereby divert current from 1 said source through said current path and said first path,

switching means to interrupt said first path following the removal of said shunt path from said are extinguishing means and said current rectifier.

References Cited in the file of this patent UNITED STATES PATENTS 1,323,327 Slepian Dec. 2, 1919 1,939,019 Ourieflf Dec. 12, 1933 2,465,682 Goldstein Mar. 29, 1949 2,610,231 Wettstein Sept. 9, 1952 FOREIGN PATENTS 113,439 Sweden Mar. 13, 1945 511,702 Great Britain Aug. 23, 1939 729,622 Germany Dec. 19, 1942 

